The present invention relates to a method of strengthening a particulate matrix, comprising embedding pieces or strips of flexible, open mesh structure in the matrix. The word "strengthening" includes reinforcing and/or stabilizing.
In general terms the matrix can be any particulate matrix, whether load-bearing or not. The structures formed can be for instance geotechnical structures, structural components for building, or surfacing materials. The maxtrix can be of any suitable form, such as soil (which includes rocks, stones, gravels, sands, clays, silts and the like as well as cement-stabilised soil and cement-bound granular materials (normally containing 2-12% cement), wastes such as mine spoil or slag, and hydraulic fills), substances comprising a hydrocarbon binder such as asphalt, bituminous asphalt or tar, substances comprising a hydraulic binder or fill, such as cement, concrete, lean-mix concrete or plaster (which are considered as particulate), substances comprising a pozzolanic binder, and substances comprising a resinous binder, such as chip-board. The matrix can be particulate and non-cohesive or cohesive, or inherently substantially rigid; a material such as clay or tar may be viscous and capable of large movement or deformation, or a material such as cement or concrete can be rigid and incapable of large movement or deformation. particulate matrices will have natural void spaces which can be filled for instance with water and/or air.
GB No. 2 073 090A describes a method of strengthening soils in which long and fairly wide lengths of flexible plastics material mesh structure are embedded in the matrix, the lengths being in parallel layers and the lengths being parallel to each other in each layer so as to cover all of the layer. The mesh structure has tenaceous junctions or intersections and has high dimensional stability in the plane of the structure. This method is very effective in most applications, but does require skill and care in use, as well as requiring a specially manufactured mesh structure.
CH No. 592 219 discloses a method of strengthening cement, tar or bitumen, comprising randomly embedding in the matrix a large number of flexible pieces of plastics material mesh structure without creating a substantial amount of extra void space, each face of each piece having an area which is small relative to the size of the matrix, and each piece comprising more than one mesh opening. However, the pieces are initially supplied in the form of short, twisted cords which are arranged to open or untwist during mixing; mixing must be so timed that the cords have fully untwisted, but have not started to twist or otherwise close up again. lt is believed that it would be very difficult to ensure that the cord untwists and opens up adequately, and very difficult to avoid any opened-up pieces closing up again--the pieces would have a tendency to roll up if there is any rolling motion during mixing (which normally occurs). In addition, it appears that the mesh structure is produced by forming parallel slits in plastics material film and then opening the film up by pulling it transversly, possibly with some heat setting. This structure would have little transverse strength, and would act as a very poor reinforcement.
An article on pages 47 to 52 in C. R. Coll. Int. Renforcement des Sols, paris 1979, discloses small strips for strengthening soil, but the strips do not give the optimum reinforcing effect as they have no significant transverse strength and would have a poor purchase on the soil.
GB No. 1 539 898 discloses the use of pieces of steel weld mesh to strengthen concrete, each piece having just one complete mesh. The pieces are relatively stiff and each has eight projecting wires, so that there will be a tendency to bridge and form extra void space.
In Ep No. 0 017 548A and in Volume III of the "proceedings of the Second lnternational Conference on Geotextiles", pages 721 to 726, there is a disclosure of such a method, mainly in connection with strengthening soil. The preferred element is a highly flexible yarn, but a close-weave strip can alternatively be used. There is however a very poor interlock between the surface of the strip itself and the soil; it is believed that the primary strengthening effect is obtained by the looping round of the strip and engagement of the soil in this manner. The distribution of the strip also appears to be mainly in horizontal planes, with small radius curves in each plane (i.e. about vertical axes), giving poor anchoring of one layer into the layers above and below. Furthermore, the strip will tend to roll or to twist or condense into a rope-like shape, reducing the surface area available for engaging the soil and tending to create extra void space in the soil.